How Vitamins Work(1/2)

 We're learning more all the time about the many ways vitamins benefit our bodies 

  Every day of your life, chances are, you think about vitamins. You read about vitamin content on the nutritional label of every food you eat. Breakfast cereals and many drinks talk about vitamins right on the label. You may even take a vitamin pill when you wake up.
  It all begs the question: what, exactly, is a vitamin? Vitamin C, for example: What is it? And why do you need to "take" vitamin C every day?
  Here is the basic definition of a vitamin: a small molecule that your body must have in order to carry out a certain chemical reaction. In some cases your body has no way to create vitamin molecules itself, so the vitamin molecules must come in through the food that you eat. In other cases your body has a way to make a vitamin molecule, but may not make enough. The human body is known to need at least 13 different vitamin molecules.
  The necessity for certain vitamins
  For example, your body needs vitamin C for several reasons, but most importantly for collagen. When your body produces collagen, it performs a chain of chemical reactions, and the vitamin C molecule is an essential part of the chain. Since collagen is used in everything from skin to blood vessels, you can see how important vitamin C can be. Without it, your blood vessels weaken, your teeth start to fall out and you eventually fall apart and die from a lack of collagen-all because of one missing molecule.
  Vitamin D is another simple molecule that is incredibly important. We actually have the ability to produce vitamin D in our skin with regular exposure to the sun's ultraviolet rays. Without enough sun exposure, people get different ailments. In children, a lack of the vitamin D molecule causes rickets , which softens the bones and causes them to deform or break easily.

Vocabulary Focus
chances are (phr) ---it is likely that
beg the question (idiom) ---to assume something that hasn't been proven
fall apart (phr. v) ---to fail or stop working effectively
ailment (n) ---an illness
Specialized terms
nutritional label (n. phr)---营养成分标示 information provided on the packaging of food products, which tells about the vitamins, minerals and other particular elements that the food item contains
molecule (n)---分子 the simpled unit of a chemical substance, usually a group of two or more atoms
chemical reaction (n. phr)---化学反应 a process in which the atomic or molecular structure of a substance is changed
collagen (n)---胶原蛋白 a protein found especially in the joints of humans and animals
ultraviolet rays (n. phr)---紫外线 invisible streams of solar light that can cause damage to living tissue